IS 12889 ( Part 2 ) : 1989 Indian Standard ( Reaffirmed 2001 ) METHODS FOR DETERMINATION OF VISCOSITY AND VISCOMETRTC FIXED POINTS OF GLASS PART 2 DETERMINATION OF SOFTENING POINT UDC 666'11'01 : 532'13 : 536'421'2 @ BIS 1990 BUREAU MANAK OF BHAVAN, INDIAN STANDARDS ZAFAR MARG 9 BANADUR SHAH NEW DELHI I I0002 June 1990 Price Group 2 Glassware Sectional Committee, CDC 10 FOREWORD This Indian Standard ( Part 2 ) was adopted by the Bureau of Indian Standards on 28 November 1989, after the draft finalized by the Glassware Sectional Committee had been approved by the Chemical Division Council. This standard forms Part 2 of Methods for determination of viscosity and viscometric fixed points of glass. Part 1 of this standard deals with dekrmination of viscosity by fibre elongation method, Softening point of glass is the temperature at which glass deforms under its own weight. It is useful as acontrol parameter, as it is closely linked with the composition of a glass type. It acquires added importance from the viewpoint of acceptance of a glass type and also in research and development studies. This standard is based on IS0 7884 - 6 : 1985 `Glass Determination of softening point'. For the purpose of deciding whether a particular final value, observed or calculated, expressing the accordance with IS 2 : 1960 `Rules for rounding significant places retained in the rounded off value this standard. Viscosity and viscometric fixed points, Part 6 requirement of this standard is complied with, the result of a test or analysis, shall be rounded off in off numerical values ( revised )`. The number of should be the same as that of the specified value in IS 12869 ( Part 2 ) : 1989 Indian Standard METHODS FOR DETERMINATION OF VISCOSITY AND VISCOMETRIC FIXED POINTS OF GLASS PART 2 DETERMINATION OF SOFTENING 1 SCOPE 1.1 This standard ( Part 2 ) prescribes the method of determining the softening point of glass. 2 REFERENCES 2.1 The following Indian Standards adjuncts to this standard: IS No. are necessary POINT and are described as follows: Furnace top made of asbestos-cement sheet, one number, 12'7 mm thick by 100 mm diameter, drilled 12-7 mm diameter at centre with three 5'6 mm diameter holes for tie rods spaced 120" apart on an 82'5 mm circle; also, two small holes suitably placed for thermocouple wires and two binding posts with nearby small holes for passage of heater wires. Spacer rings made of asbestos-cement sheet, two numbers 12'7 mm thick by 94 mm outside diameter by 70 mm inside diameter, drilled 5.6 mm diameter for tie rods. Webs made of asbestos-cement sheet, two numbers, 6'5 mm thick by 94 mm diameter, drilled 19 mm hole at centre and six 19 mm holes 60" apart on 51 mm circle; also drilled 5.6 mm diameter for tie rods. Furnace core made of nickel, one number, 95 mm height by 29 mm diameter, with 6'5 mm at each end turned to 19 mm diameter. Entire length drilled at centre 5'6 mm diameter and symmetrically drilled 3'2 to 5'6 mm diameter from each end to depth of 47'5, as near to centre hole as possible. Core wrapping, thickness. made of mica, double Title Thermocouples 7358 : 1984 12869 Methods for determination of ( Part 1 ) : 1989 viscometric fixed points of glass: Part 1 Determination of viscosity by fibre elongation method 3 FIELD OF APPLICATION 3.1 Method prescribed in this standard is applicable to all glasses of normal bulk production compositions unless devitrification takes place during the preparation or testing of the specimen, The softening points range between 370 and 1 OOOC, depending on the type of glass. 4 TERMINOLOGY 4.1 For the purpose of this standard, the definitions given in IS 12869 ( Part 1 ) : 1989 shall apply. 5 PRINCIPLE 5.1 Determination of the temperature at which a round fibre of the glass, nominally 0'65 mm in diameter and 235 mm long with specified talerances, elongates under its own weight at a rate of 1 mm/min when the upper 100 mm of its length is heated in a specified furnace at the rate of 5 fl"C/min. 6 APPARATUS 6.1 Furnace The furnace shall conform to all essential details illustrated in Fig. 1. Various parts are numbered 1 Winding made of No. 20 nichrome wire ( 80% nickel, 20% chromium ) of power 1 k W, wound round the whole length of furnace core. Alundum cement coating. Insulation, consisting of diatomaceous or equivalent. earth Furnace bottom made of asbestos-cement sheet, one number, 12'7 mm thick by 115 mm in diameter. Drill at centre a hole of 12'7 mm diameter, 6'4 mm deep from top; finish through at 5'6 mm diameter. Drill three holes for tie rods 120" apart on 82'5 mm circle, 12'7 mm diameter, 6'4 mm deep from bottom, finish IS 12869 ( Part 2 j : 1989 through at 5.`6 mm diameter. 5'6 mm holes on 105 mm circle. Drill three JO Plate made of steel, one number, 6 mm thick by 115 mm diameter securely fastened ( for example, welded ) to lower chamber, with three holes to match edge holes of furnace bottom. Drilled at centre 5'6 mm diameter. 11 Glass samples, 235 &I*0 mm in Iength, exclusive of bead at top end, and 0'65 f0'10 mm in diameter, uniform to 0'02 mm. I2 Lower chamber made of galvanized sheet steel or preferabIy stainless sheet steel, one number consisting of cylinder 200 mm long and 80 mm diameter, carrying a flat glass window 60 mm by I50 mm. I3 Bottom plate made of steel, one number, 8 mm by 150 mm diameter, securely fastened ( for example, welded ) to lower chamber and carrying three levelling screws on 135 mm circle. I4 Cylinder made of asbestos-cement sheet, one number, 19 mm high by 12'7 mm outside diameter by 3'2 mm inside diameter, with tapered hole at top as shown. 15 Tie rods made of steel, three number, 4 mm by 153 mm, tbreaded at both ends. 16 Furnace shall be made of gaivanized sheet steel or preferably stainless sheet steel, one number, 95 mm inside diameter by 122 mm long, welded. I7 Double-bore ceramic tubing made of porcelain, one number, 3 to 5 mm diameter. First insert 3 to 4 mm length to isolate thermocouple from core ( see4 ). I8 Cylinder made of asbestos-cement sheet, one number, 19 mm high by 12'7 mm outside diameter by 3'2 mm iuside diameter, relieved at bottom for thermocouple wires. 19 Fibre support made of brass, one number, 60 mm by 12 mm by 3 mm, with 0'8 mm hole on centre line 6.4 mm from one end and 6'4 mm hole at other end, the holes to be 40'4 mm apart on centres. Furnace sample holder fixed by one of tie rods should not touch upper furnace wall ( distance 2 to 3 mm ), SO that changes of dilation of the furnace core are not transmitted to them, 20 Thermocouple leads. 2 FIG. 1 DETAILS OF SOFTENINGPOINT FURNACE 6.2 Furnace Stand A means shall be provided for supporting the furnace so that the fibre hangs below it. This stand shall be provided with a levelling device such as three screws. The stand shown in Fig. 1 is convenient when used with either a cathetometer or a telescope and scale. 6.3 Heating Rate Controller Suitable controls shall be provided for maintaining the furnace heating rate at 5f l"C/minute. NOTE - A continuously adjustabletransformerhas proved effective for controlling the heating rate. 6.4 Temperature Measuring meots and Indicating Instru- 6.4.1 The platinum 10 percent rhodium/platinum ( type S according to IS 7358 : 1984 ) thermocouple, or nickel-chromium/nickel ( Type K according to IS 7358 : 1984 ) thermocouples placed in a double bored porcelain tube in accordance with the diagram in the Fig. 1 shall IS 12869 ( Part 2 ) : 1989 exhibit low thermal inertia, the diameter wires should not be greater than 0'5 mm. of the 6.4.2 The measurement thermocouple shall be placed in the furnace core in accordance with the specification in Fig. 1 ( No. 4 and 17 ). The thermocouples shall be calibrated in accordance with IS 7358 : 1984. 6.4.3 The electrical output of the thermocouples shall be determined at zero current by means of or high-resistance electronic potentiometers, amplifiers having a sensitivity of 1 V for Type S according to IS 7358 : 1984 or 4 V for Type K according to IS 7358 : 1984. Precautions shall be taken that the ice-bath for the cold junction is maintained at 0°C throughout the test. If the temperature measuring equipment is fitted with autothe ice-bath matic cold junction compensation, can be omitted. 6.5 Fibre Elongation Measurement Equipment The fibre elongation shall be measured by a device capable of measuring the position of the end of the fibre within 0'02 mm throughout the entire elongation period. NOTE - Suitable devices that have proved effective for measuring the elongation are of both optical and electronic types. For some devices it may be convenient if they are fixed with the furnace stand. for example by ashort optical bench. fused silica ) and flame-working the sample until the glass is sufficiently fluid to be drawn into a fibre. If the sample is in long stick form, it may be flamed-worked directly without attaching it to a handle. Acceptable fibre sections may then be broken from the fibre and a bead formed on one end of the fibre section by fusing in the flame. The opposite end shall then be broken to the specified length and the tip may be fire polished if desired. Fibres may also be drawn by any suitable device. 8 PROCEDURE 8.1 Calibration with Standard Glass Calibration of the apparatus shall be done by measuring in duplicate the softening point of appropriate reference glass(es), the softening points of which are near to that of the test glass. Compute the difference between the average measured softening point and the certified softening point for the reference glass(es) and the average of these differences. If the average difference from the certified values is greater than l"C, add' or subtract this difference as a correction to the measured softening points of the unknown glasses. 8.2 Measurement 8.2.1 To equalize the heat distribution of the furnace, heat the fibre furnace to about 30°C above the expected softening point of the glass under test. Then cool the furnace to about 20°C below the expected softening point, and adjust the settings on the heating rate controller to obtain a heating rate of 5f l"C/minute. 8.2.2 Again, cool and hold the furnace about 20°C below the expected softening point, and insert the fibre in the furnace by placing the bead end in the furnace sample holder. Check the fibre to be certain that it is hanging freely in the centre of the furnace, and re-level the furnace, if necessary. Prepare the temperature measuring equipment and adjust the elongation measuring equipment. 8.2.3 Set the furnace control for a heating rate of Sfl"C/minute. Observe the fibre as the furnace heats, and when it begins to elongate at the rate of approximately 0'1 mm/minute, start recording the fibre: length to within 0'02 mm. Take a length reading at the end of each minute and take the temperature of the furnace at each 1 minute interval, displaced with respect to the length readings by 0'5 minute. Continue to read and record the length and the temperature until the elongation becomes 1'2 mm or greater in a 1 minute interval. When the elongation exceeds 1'2 mm in a 1 minute interval, remove the fibre and cool the furnace in readiness for a duplicate 3 6.6 Fibre Diameter Measurement Equipment The fibre diameter shall be measured meter with 0'01 mm divisions. 6.7 Timer A timing device with a least count of one second shall be used. 7 PREPARATION and accuracy by micro- OF TEST SPECIMENS 7.1 The fibre specimen used for the test shall meet the following requirements: a) It shall be round; b) It shall be smooth and shall contain voids or foreign matter; no c) Its average diameter shall be 0'65fO'lO mm shall not and the maximum diameter exceed the minimum diameter by more than 0 02 mm over the entire length of the fibre; and 4 It shall including be 235fl'O mm the top bead. in length, not 7.2 A test fibre conforming to these requirements may be drawn by attaching ;I clean sample of the glass under test between two non-fusible rods ( such as platinum-group alloys, porcelain or IS 12869 ( Part 2 ) :1989 run. An alternative acceptable method is to read the length at 1 minute and 0'5 minute intervals and the temperature at the 0'25 and 0'75 minute intervals continuing to read and record length and temperature until the elongation becomes 0'6 mm or greater ia a 0'5 minute period. 9 EXPRESSION OF RESULTS repeat fibres. the complete test with two naqr 10 TEST REPORT 10.1 The test report shall include: a) reference to Indian Standard; b) description of the sample; c) method of sampling; d) number of test specimens; e) method of preparation; f) type of softening point apparatus used; 8) method of calculation; h) corrections applied; in j) softening point temperature Celsius : mean of both runs; and degrees 9.1 Determine the temperature at which the elongation is 1 mm/minute. This may be done by plotting or graph as follows: a) Plot the data on semi-log paper, with the potentiometer or temperature readings on the uniform scale, and the difference between length readings per unit time on the log-scale. The point where a straight line drawn through the data points crosses the 1'0 mm]minute line shall be as the indicated softening point. Make the calibration corrections as specified in 7.1, if necessary. b) If the difference between the results for two fibres evaluated is greater than 2°C k) any change in the glass observed during and/or after the test. 4 Standard Mark The use of the Standard Mark is governed by the provisions of the Buremr of Indian The Standard Mark on Standards Act, 1986 and the Rules and Regulations made thereunder. products covered by an Indian Standard conveys the assurance that they have been produced to comply with the requirements of that standard under a well defined system of inspection, testing and quality control which is devised and supervised by BIS and operated by the producer. Standard marked products are also continuously checked by BIS for conformity to that standard as a further safeguard. Details of conditions under which a licence for the use of the Standard Mark may be granted to manufacturers or producers may be obtained from the Bureau of Indian Standards. Bureau of Indian Standards BIS is a statutory institution established under the Bureau of hdkm St&rds Act, 1986 to promote harmonious development of the activities of standardization, marking and quality certification of goods and attending to connected matters in the country. Copyright BIS has the copyright of all its publications. No part of these publications may be reproduced in any form without the prior permission in writing of BIS. This does not preclude the free use, in the course of implementing the standard, of necessary details, such as symbols and sizes, type or grade designations. Enquiries relating to copyright be addressed to the Director ( Publications ), BIS. RevMoo of Indian Standards Indian Standards are reviewed periodically and revised, when necessary and amendments, if any, are issued from time to time. Users of Indian Standards should ascertain that they are in possession of the latest amendments or edifion. 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